Bi-level lighting includes two lighting levels, with one level being at or near 100% of available light output and the other level being significantly less than 100% of available light output. Energy codes in the United States and other countries generally require multi-level lighting control for various lighting applications to conserve energy during periods of no occupancy. During periods of occupancy a full lighting level is applied. To be compliant during periods of no occupancy, less than the full lighting level is applied. These energy codes are applicable to various lighting applications, for example, those requiring continuous lighting. For example, an interior stairwell, parking garage, or parking lot require the full lighting level when occupied and less than the full lighting level when not occupied.
A prior art 0-10 VDC dimming controller 56 associated with a light fixture 50 is illustrated in FIG. 1. The light fixture includes a driver 52, driver output 53 and lamp 54. The driver 52 includes a 0-10 VDC dimming control input 57 connected to the prior art dimming controller 56. The driver 52 also includes a power input 59 connected to an AC power source 58. Typical prior art 0-10 VDC dimming controllers provide a 0-10 VDC dimming input signal based in part on an expected input impedance of the driver it is associated with. If the output impedance of the prior art dimming controller 56 and the input impedance of the 0-10 VDC dimming control input 57 of the driver 52 are incompatible, the driver output signal 53 coupled to lamp 54 may provide a brighter or dimmer light level than expected due to this impedance incompatibility.
Some light level controllers, including bi-level lighting controllers require a minimum load to function as expected, for example, three or more light drivers coupled to the controller. Other bi-level lighting solutions simply switch off some but not all of the lighting fixtures; however, this can generate undesirable variable lighting patterns.
Some bi-level lighting solutions include an all-in-one lighting device. For example, a device with a sensor and bi-level switching device integrated within a single structure. However, code compliance requires that low voltage wiring such as that used for bi-level switching to be run separately from higher voltage wiring used to power the lighting. Running separate low and high voltage conduits to each light fixture can be expensive and sometimes impractical, especially when retrofitting existing structures and installations.
Additionally, a low voltage 0-10 VDC bi-level controller from a particular manufacture may not be compatible with a 0-10 VDC dimming control input for a driver from a different manufacture, due to different electrical configurations, for example, different input impedances, as described for the prior art dimming controller 56 illustrated in FIG. 1. For example, a driver provides a current to a bi-level controller and responds to a change in the bi-level controller based on a predetermined resistive load. If a bi-level controller provides a different predetermined resistive load, or if multiple drivers are attached in parallel to a single bi-level controller, the lighting output will likely be different than expected with compatible drivers and the bi-level controller because of the change of impedance coupled to the bi-level controller output when the 0-10 VDC dimming control inputs are wired in parallel.
More specifically, a typical 0-10 VDC dimming control input of a LED drivers and other lighting power devices (collectively “driver(s)”) is a current source with an impedance designed such that the voltage drop across the dimming input is 10 VDC when no dimming controller is connected to the driver. Connecting an impedance source as a dimming controller across the dimming input, for example, a fixed or variable resistor, or a 0-10 VDC power supply, provides an input impedance across the dimming input that is less than the impedance of the current source, resulting in a drop in the dimming voltage across the dimming input to below 10 VDC. The resulting dimming input voltage is sensed by the internal dimming circuit of the driver, which controls the voltage output of the driver to dim the lighting proportionally to the sensed dimming input voltage.
If a fixed impedance source is used as a dimming controller for more than one driver, the resulting dim level for the lighting may be different for a selected dimming level when the dimming controller is connected to a different driver or to a different number of drivers with dimming inputs connected in parallel. When different or multiple driver are connected in parallel the impedance of their dimming control input(s) may change relative to the static impedance for the dimming level set by the dimming controller connected across their dimming control input(s). Also, the total current supplied by the one or more current sources changes when a different or multiple parallel connected dimming control inputs are delivered to the dimming controller. Even though no change has been made in the dimming controller to change the dimming level, the change in impedance and/or current presented to the internal dimming circuit of the driver results in a change in the voltage across the dimming control input(s) and an unintended change to the resulting output of drivers dimming the lights to a different level than for a single driver or different drivers connected to the dimming controller.
Additionally, lighting applications requiring selectively switching between a preset selected dimming level and no dimming (full-on) are generally based on a control signal other than the 0-10 VDC proportional dimming signal, for example, an output of an occupancy or daylight detection sensor. Condition detection sensors typically provide a relay output that is normally open and is closed upon detection of a condition. The relay is typically used to switch the 120 VAC supply provided to one or more lighting drivers. In this configuration, the lighting can be controlled to switch the driver and lighting between off and full-on, or between off and a preset dim level; however, the configuration does not accommodate switching between a preset dim level and full-on.